A hybrid log antenna system is an antenna system which includes a low frequency element described combined with a log periodic dipole array. In a conventional arrangement, the low frequency element is a bow-tie or Brown-Woodward Dipole antenna 10, shown schematically in FIG. 1.
A well known variant on the bow-tie antenna of FIG. 1 is the tapered, inverted-L geometry. An inverted-L geometry is obtained by taking a conventional wire dipole and bending the two straight elements to provide two L-shaped elements. This greatly reduces the overall width of the dipole while only slightly degrading the electrical performance (resonance frequency and bandwidth). Thus it provides a better performance-to-size ratio. A tapered, inverted-L geometry is obtained by taking a tapered dipole, bow-tie, or Brown-Woodward dipole and bending it into two L-shaped pieces in a similar fashion. A perspective schematic view of such a tapered, inverted-L antenna 20 is shown in FIG. 2a. A top view of the antenna of FIG. 2a is shown in FIG. 2b.
A problem with this antenna design, however, is the relatively large capacitive reactance, especially when compared to the resistive component of the input impedance which is exhibited by the electrically-short dipole. Another drawback to the tapered, inverted-L antenna is that matching the impedance of the antenna to the signal generator is difficult. A conventional 1.5 meter tapered, inverted L-Antenna configured to operate at a frequency of about 25 MHZ has an input impedance of around 5 ohms, making it difficult to match the antenna to components having a conventional 50 ohm input impedance. A mismatched impedance limits the efficiency and power transfer of the antenna/matching network and thus the overall efficiency of the system.
Accordingly, it would be advantageous to provide an improved tapered, inverted-L bow-tie antenna assembly which has lower capacitive reactance than conventional designs and also provides for better impedance matching.